Because the sun is obviously the star closest to the Earth, it is often excluded from lists of stars near our planet, with lists beginning with Proxima Centauri or the second closest star to the Earth. Following this tradition and excluding the sun, three stars closest to the Earth technically consist of two stars, the last two belonging in a binary star system and therefore considered as one. More than four light years away, the closest neighbors to the Earth include Proxima Centauri and Alpha Centauri A and B, all members of the constellation Centaurus.
Besides the sun, the closest star to the Earth is Proxima Centauri, discovered in 1915 by the director of the Union Observatory in South Africa. The director, Robert Innes, proposed the star be named with the Latin root “proxima,” which means “next to,” due to it’s closeness with Alpha Centauri. In diameter, the Proxima Centauri is about 1/7 that of the sun and about 1.5 times the diameter of Jupiter. As the name may suggest, it is also a part of the constellation Centaurus, or an ancient celestial depiction of a centaur. Proxima Centauri is not exceptionally bright and despite being the star closest to the Earth cannot be seen by the naked eye. However, the star sometimes experiences dramatic and beautiful solar flares observable by telescope, 4.2 light years away.
Alpha Centauri A
Alpha Centauri A is the largest star in the binary star system known as Alpha Centauri and what is considered the second star closest to the Earth. Although the star closest to Earth cannot be seen by the naked eye as it is a small red dwarf, Alpha Centauri A is a yellow star and therefore visible without any equipment. Because it is in a binary star system, Alpha Centauri A is one of two stars orbiting around a common center of mass, together appearing as a single celestial object from Earth. Compared to the sun, the star is about 10 percent more massive and about 23 percent larger in radius, as well as being more luminous than the sun and being the fourth largest star in the sky after the sun.
Alpha Cantauri B
The Alpha Centauri binary star system also includes Alpha Centauri B. Though slightly smaller than Alpha Centauri A, it still has 90 percent of the sun’s mass and only a 14 percent smaller radius. As such, it is less luminous than its sister star. But it sometimes emits higher energy X-rays than its counterpart. Although the two second closest stars to the Earth oscillate between being as far away from one another as the sun and Saturn and the sun and Pluto, Alpha Centauri A and B appear to the naked eye as a single object, showing the triviality of such a vast distance in space. Together, the Alpha Centauri are 4.3 light years away from Earth.
Faure, Gunter, and Teresa M. Mensing. Introduction to Planetary Science: The Geological Perspective . Dordrecht: Springer, 2007. Print.